landing gear position

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I am in the process of rebuilding my Magnum. I damaged the landing gear and am replacing. My Magnum came with a grove spring but Avid had built the spring brackets that interfaced between the spring and the fuselage. Those brackets are made of steel tubing and are relatively complex welded structures. They were damaged beyond repair. I ordered the Grove brackets for the Magnum to replace the original Avid ones. the grove brackets are beautiful machined aluminum pieces of art. However, the Grove brackets due to their construction move the landing gear back 1 inch from the original landing gear position.

I think have a pretty good idea of what to expect in general regarding the behavior moving the landing gear back will do. I suspect it would make the plane more susceptible to putting it on its nose during hard braking. Otherwise I can't see a down side.

My question is how much difference will an inch really make? Will it be huge or barely noticeable? Does anyone have actual experience moving landing gear and seeing the effects on a tailwheel plane?

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I am in the process of rebuilding my Magnum. I damaged the landing gear and am replacing. My Magnum came with a grove spring but Avid had built the spring brackets that interfaced between the spring and the fuselage. Those brackets are made of steel tubing and are relatively complex welded structures. They were damaged beyond repair. I ordered the Grove brackets for the Magnum to replace the original Avid ones. the grove brackets are beautiful machined aluminum pieces of art. However, the Grove brackets due to their construction move the landing gear back 1 inch from the original landing gear position.

I think have a pretty good idea of what to expect in general regarding the behavior moving the landing gear back will do. I suspect it would make the plane more susceptible to putting it on its nose during hard braking. Otherwise I can't see a down side.

My question is how much difference will an inch really make? Will it be huge or barely noticeable? Does anyone have actual experience moving landing gear and seeing the effects on a tailwheel plane?

Thanks!

Chris, I know that this might be impractical, but if the plane weighed exactly the same after the rebuild as before the rebuild, then it would be easier to figure by just weighing it. Disregarding that, lets guess at a figure of say 60 inches between center of mains and center of nosewheel - then you move the mains 1" to the rear, so you have increased the weight on the nosewheel by about 1/60 - supposing you had a nosewheel weight at normal loaded weight of 90 lbs, then you would have increased the nose weight about 1.5 lbs - Not enough to be concerned about, IMO. Now, thinking twice - You just moved the main gear weight aft by 1", so you have shifted your EW to the rear, so the weight of the gear times the arm is going to shift your CG to the rear - And I just lost my mind on this train of thought - Maybe Luke or someone else can figure it better?

Now, this is all guesstimating on my part - someone with a better calculator could have different figures...I don't think it will have any more tendency to stand on its nose - maybe even less?

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First this is a tail wheel plane. But you are right. simple math tells me how much moving the weight of the spring and tires changes the CG, but that is not what I am talking about. CG is an in flight characteristic relative to the wing. I am asking how much real world effect moving the gear back one inch might have on ground handling, mostly with respect to how much more sensitive is the plane likely to be to nose over on hard braking. I have no idea. I suppose I will learn, because that is what I will end up with, but I am looking for anyone's first hand experience.

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Chris, My Ercoupe was a lot more nose heavy than the Cessnas, and I could stand on the brakes without worry about nose-over. The only time you might have a tip-over would be hard braking in a fast turn - The more distance you have between mains and nose and wider mains lessens this chance.

And, your CG does affect ground handling, weight on nose, steering, etc. Forward CG puts more weight on nose, and a Higher CG position can contribute to tip-overs. That's where the heavy main gear is a plus.

There is a tip-over and turn radius formula listed somewhere in my books, but your distance is fixed, so it wouldn't matter.

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The bigger concern could be the yaw stability on the ground. What is your normal CG station, relative to the gear position, in inches? For my Avid Flyer MK IV the gear is -1.6" and the CG is typically +13 to +15 inches, so the CG is about 15 to 16 inches aft of the gear. Moving the gear 1" closer to the CG is a 6 to 7% improvement in yaw stability (1/15 or 1/16), and as EDMO said, an insignificant change in longitudinal ground stability. If the Magnum numbers are about the same, Have at it, I say.

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My experience with taildragger r/c planes that get their landing gear bent rearward is that it's ALWAYS better to bend them back to the original position or even a little forward to keep it from going over on its nose, and they have no brakes. Otherwise the least little ground resistance will have them on their backs like liquor in sorority girls! Leni, do you agree? Also, I think the yaw stability is going to decrease because the shorting of the distance between mains and tail. On the flip side of this argument is the ability to tame the Avids crappy short coupled handling (taildragger) by using an extended tail spring. Good luck

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The bigger concern could be the yaw stability on the ground. What is your normal CG station, relative to the gear position, in inches? For my Avid Flyer MK IV the gear is -1.6" and the CG is typically +13 to +15 inches, so the CG is about 15 to 16 inches aft of the gear. Moving the gear 1" closer to the CG is a 6 to 7% improvement in yaw stability (1/15 or 1/16), and as EDMO said, an insignificant change in longitudinal ground stability. If the Magnum numbers are about the same, Have at it, I say.

Nick, I know you have a better calculator than I have, and you are talking about a taildragger: I don't have exact dimensions for the Magnum, but the main gear should be just forward of the rear strut attach point, which would make it maybe +26" from the leading edge data point, and I am not sure what his nose wheel location is from the leading edge, but it would maybe be a minus 12" to 20" number. His main gear would be an inch farther back from the CG than now which would put a minimal additional weight on the nose wheel, and add another inch to his longitudinal wheelbase.

Nosedraggers have a positive yaw stability on the ground anyway because the CG is in front of the mains, compared to the negative yaw stability of the taildraggers.

I am sure if we had the exact numbers for the dimensions on Chris' plane, we could figure out the slight difference moving the main gear will make - But I believe his concerns will soon go away once he has it going - Then he can tell us what, if any, difference he feels.

GO WITH YOUR BUILD CHRIS - We are anxiously waiting for a report on your new Kayak Hauler!

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Dean is helping me with some aspects of my Magnum repair that I do not have the tools, skill or knowledge to do myself. (Wing spar and some fuselage repair)

I briefly spoke with him about this this weekend. He told me that the first tail wheel planes with tail skids and no brakes landed primarily in wide open spaces and into the wind. They had the landing gear right at the forward CG because it made planes the least ground loopy. He said over the years as planes started landing on pavement runways and as brakes improved the landing gear has moved progressively further forward to prevent nose over. His opinion like most others as well as mine now is that it will make some difference, but probably not a lot considering the very WIDE range of where TD landing gear has been placed over the history airplanes. So the plane should be a touch less ground loopy and a touch more prone to nose over upon hard braking on pavement.

Bottom line for me is it will be what it is and I will fly and land it the way it is! :-)

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I have been through a few different gear set ups on mine. This newest gear is extended forwards and 5" taller than the Avid Wide Gear. I cant raise the tail anymore by standing on the brakes and giving it full power and full down elevator. I don't like that. I really like being able to get the tail in the air on the really rocky gravel bars and when on ski's. I would say that moving it back 1" wont hurt you, but I would be cautious and check it out then first time you get her back out at the airport. Can you stand on the brakes and raise the tail using power and down elevator? if so, use a little caution on the braking on the first few landings till you figure out how hard you can brake when your rolling out. I would doubt your in much danger of nosing over unless your REALLY trying to get in short and compete at Valdez or some other STOL contest

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I could raise the tail and taxi around or raise the tail and take off from standstill previously, but it wasn't very easy. It took a shitload of power and I never felt as "comfortable" doing it as the hotshots make it look. So I will see how much easier the tail raises with power with the new mounts moving the gear back an inch. That will really provide good information and give me a feel for how it will behave.

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EDMO, Chris has a taildragger, he asked, " Does anyone have actual experience moving landing gear and seeing the effects on a tailwheel plane?"

Nick, I guess I totally missed the boat on this one - Chris and I have been talking and posting about nosewheels for so long I thought he was still in that mode. I thought this was because his plane was originally a taildragger and now converted. Does ChrisB now have TWO planes, and one is a taildragger? EDMO

Edited 19 Nov 2015 by EDMO

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I have two planes. An Avid Magnum tail wheel and a Fat Avid nose wheel. Neither is flying right now. I've been working in the Fat Avid thinking I can get it in the air first, but recently I've put a burst of work into the Magnum and it is catching up.

Sorry for the confusion.

Chris

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I have two planes. An Avid Magnum tail wheel and a Fat Avid nose wheel. Neither is flying right now. I've been working in the Fat Avid thinking I can get it in the air first, but recently I've put a burst of work into the Magnum and it is catching up.

Sorry for the confusion.

Chris

Thanks for clearing this up for me Chris - I was beginning to think maybe I needed some Alzheimer pills !!! Hope you are back to flying soon, whichever comes first.